Related Stories

Scientists think they may have solved one of the great mysteries of the Solar System: why the winds on Venus blow faster than the planet's rotation?

Venus rotates once every 243 Earth days, but it takes just 4 Earth days for clouds in the Venusian atmosphere to go all the way round the planet at speeds of 200 metres per second.

This phenomenon, known as superrotation, is only known to commonly occur on Venus and the Saturnian moon Titan.

Astrophysicists have long speculated that temperature differences between the day and night time sides of Venus is what drives these winds.

The viscosity of Venus's atmosphere should be enough to dissipate this energy and slow the winds down.

But that's not happening, so something else must be injecting energy into the system to keep things going as fast as they seem to be.

Ionic winds

Now a team of scientists led by Hector Javier Durand-Manterola from the Universidad Nacional Autonoma de Mexico says the winds are being driven by another much faster wind flow, higher above the planet.

Reporting in the physics blog ArXiv.com Durand-Manterola says winds in the ionosphere between 150 and 800 kilometres above the surface play an important role in superrotation.

These ionic winds were discovered by the American Pioneer Venus Orbiter in the early 1980s.

Transterminator flow

Known as the transterminator flow, the winds travel at supersonic speeds of several kilometres per second, and are thought to be driven by the planet's interaction with solar winds from the Sun.

Durand-Manterola says the supersonic winds in the ionosphere generate sound waves through turbulence, which inject additional energy into the atmosphere.

The researchers say their calculations indicate the process puts in more than enough energy to account for the amount lost due to atmospheric viscosity.

They predict the sound waves created by the energy injection have an intensity of 84 dB.

To back up their theory, they performed a simple experiment with water to show how the energy transfer occurs.

Twisted sister

Venus is often called the Earth's sister planet because both are similar in size, gravity and composition.

But if Venus is our sister it's a twisted sister.

The surface temperature is hot enough to melt lead, it has a dense carbon dioxide atmosphere with an average surface air pressure 92 times that on Earth and a thick planetary cloud cover that rains sulfuric acid instead of water.

Australian planetary scientist Dr Andrew Prentice from Melbourne's Monash University says the new research makes "interesting reading" but was surprised that data from the Venus Express mission wasn't included in the work.

Prentice says he's looking forward to seeing peer review of the paper and finds it interesting that this mechanism hasn't been considered before.

Japan's Akatsuki spacecraft, which was launched on an H-2A rocket from the Tanegashima Space Centre south of Tokyo a few days ago, is now on its way to Venus.

When it arrives in December, it may help provide a few answers to this enduring mystery.